Components vendors and providers of wavelengths division multiplexing (WDM) optical systems are under great pressure to provide cost relief by developing ways to reduce capital and operating expenditures. Capital expenditure savings can be achieved, e.g. through overall reduction in optical components and associated costs. The operating expenditure savings can be achieved by developing components that are simpler and easier to maintain, requires fewer repairs, take up less space and consume less power.
In WDM network electronically controlled variable optical attenuators (eVOAs) are widely used to control optical signal power. The eVOAs are deployed either before and/or after lasers to attenuate an incoming and transmitted light to compensate for laser power drift and to prevent over-saturation at the receiver end. When wavelengths are added, dropped or routed in an optical network, an eVOA inserted in the optical signal path can manage the optical power fluctuations of the processed signal. As the number of channels to be monitored in the network increases, it drives the significant changes in eVOAs requirements that include the need for multiple eVOAs, the need for electronic control and the need for speed.
FIG. 1 shows a prior art arrangement including a plurality of eVOAs 120, 125, 130, 135, 140, 145, 150 and 155, and optical tap couplers and tap monitors 101 to 116. Each of the channels (wavelengths) 181 to 188, has an optical tap coupler and tap monitors that leads the eVOAs and another optical tap couples and tap monitor that follows said eVOAs, e.g. optical coupler and tap monitors 101 to 108 lead the eVOAs 120 to 155 respectively, and optical coupler and tap monitors 109 to 116 follow said eVOAs.
FIG. 2 shows a prior art optical system 200 including the arrangement of the plurality of eVOAs of FIG. 1. The optical system 200 can be, for example, an optical add/drop multiplexer or part thereof, a cross-connect optical add/drop node or an optical switching system. Referring to FIG. 2, a plurality of optical tap couplers and tap monitors 201 to 208 respectively lead multiple eVOAs 220, 225, 230, 235, 240, 245, 250 and 255, and another plurality of optical tap couplers and tap monitors 209 to 216 follow said eVOAs. A WDM optical signal input 280 is received by the optical system 200 at a microcontroller 260, and the de-multiplexed wavelengths are fed to the optical tap couplers and tap monitors 201 to 208 for detecting and measuring the optical signal power at the inputs to the eVOAs 220, 225, 230, 235, 240, 245, 250 and 255 respectively. The optical tap couplers and tap monitors 209 to 216 that follow said eVOAs are for detecting and measuring the optical signal power at the outputs of the respective eVOAs. The system 200 shows “n” eVOAs, where “n=8” in FIG. 2, wherein each eVOA requires an individual control circuit (one of the circuits 261 to 268) and an adjustment circuit (one of the circuits 271 to 278), which control each individual eVOA with different attenuation for each of the channels (wavelengths) 281 to 288. The channels (wavelengths) 281 to 288 are then multiplexed by a multiplexer 295 to form a WDM output 290. In the system 200 the Processor 270 communicates with the control and adjustment circuits 261 to 268 and 271 to 278 for individual eVOAs to control the amount of attenuation for their respective output signals.
As the number of channels (wavelengths) in the optical system 200 increases, the number of eVOAs increases and, in turn, the number of eVOA control and adjustment circuits increase, which results in an increased load on the microcontroller 260 to provide appropriate attenuation setting for multiple eVOAs. As a result, the total number of the required components increases, which lead to the increase in the initial installation cost, space and power consumptions of the optical system.
Accordingly, there is a need to provide an improved methods and systems for operating and controlling a plurality eVOAs, which would reduce initial installation cost, consume less power and occupy less space, while ensuring efficient attenuation of optical signals in an optical network and provide adequate protection of optical equipment in the network.